The active site chemistries of two iron-containing dioxygenases, called lipoxygenases, are carefully examined to provide new insight into the mechanisms of these enzymes and to provide new methods to control enzyme activities. A readily available lipoxygenase from plant sources and the lipoxygenase from human platelets will be the enzymes to be studied. The mechanism of the enzyme-catalyzed reactions in each case will be fully explored to determine the roles in this reaction of the iron atom, molecular oxygen and other active site functions. Further, the mechanism of enzyme-activation by the product will be probed as a possible way of developing new enzyme activators. Finally, the irreversible inactivation of the enzyme by "mechanism-based" inhibitors will be carried out. The goal is to better understand now these irreversible inhibitors are generated at the active site in an enzyme-catalyzed reaction. This might lead to insight into the mechanism of enzyme catalysis and might lead to new ways to inhibit the enzyme. The development of new and highly selective enzyme activators and inactivators might result in the development of new pharmacological probes for the roles of the products of lipoxygenases in vivo and to new anti-inflammatory drugs.